Pleated paper filter elements of the type used in forced air systems require replacement as soon as the surfaces are covered by dust and dirt particles which clog the paper filter, prevent further filtration and restrict air flow. For a given air flow and dust or dirt concentration, the useful life of the filter or time between cleaning depends on its surface area. Thus, to increase the useful life of a filter element, the surface area is typically increased.
Depending upon the application, filter life and size are varied in relation to each other and cost. However, it would be desirable to provide a pre-filter device which can be inexpensively added to a pleated paper air filter to increase the useful life of a filter element having a given area. It would also be desirable to provide a reusable and cleanable polypropylene screen configured to pre-filter the air stream passing through the paper filter to remove large particles and thereby prolong the life of the air filter.
It would also be desirable to provide an improved pre-filter which is seated tightly on the main filter and, depending upon the application, separable from the main filter.